The present disclosure relates to a method for producing fresh milk having a longer shelf life.
In a general method for producing drinking milk, see FIG. 1, raw milk is first heated to a preset skimming temperature. This can be, for example, between 55 and 62° C., in order to prevent protein damage.
After the skimming, that is to say separating the raw milk into cream and skimmed milk, the cream is homogenized.
Then the skimmed milk is optionally standardized by adding a predetermined amount of homogenized cream.
Hereafter, the standardized and homogenized milk must be pasteurized at a temperature between 72° C. and 75° C. and for a treatment time of 15 seconds to 30 seconds. In this step, spoilage-relevant germs are killed.
Finally, the milk is cooled to a temperature of 6-7° C. Such a method of production, with aseptic packaging, ensures a shelf life of up to 12 days.
In addition, a great variety of methods are known which ensure an extended shelf life of milk. Usually, high-temperature heat-treated milk, however, exhibits significant taste differences compared with fresh milk.
For instance, what is termed extended shelf life, or ESL, milk is known which has a shelf life of at least 20 days at storage temperatures T≤8° C.
An important precondition for a longer shelf life of milk is a great germ reduction of spore formers and a reduction of the total germ count. These accelerate the spoilage of milk to a great extent.
Known methods which are used in the production of ESL milk are described hereinafter.
ESL Direct Heating System:
As starting product, standardized and thermally treated milk or only fat-standardized milk is provided in a store.
In the direct heating system, the product is regeneratively heated to 70° C. to 85° C. and then heated to a maximum of 127° C. by direct steam injection. After hot-holding the milk for 3 seconds, it is cooled in a flash cooler to 70° C. to 85° C. Aseptic homogenization at 70° C. then follows.
ESL Indirect Heating System:
As starting product, the same product as in the direct heating is provided in a store. The milk is regeneratively heated to 70° C. and then septically homogenized. The product is then heated to 105° C. to 107° C. in the regenerative heat exchanger and heated in the heater section to 127° C. for 2 seconds.
ESL Microfiltration:
The raw milk here is separated at the usual skimming temperature of 55° C. The skimmed milk is then microfiltered likewise at 55° C. The cream can be heated with the retentate in the course of 6 seconds to 105° C. to 125° C. and mixed with the skimmed milk and homogenized. The milk is then pasteurized and cooled to 4° C. to 6° C.
Membranes having pore sizes of 0.8 μm to 1.4 μm are used which are said to guarantee a germ retention greater than 99.5%. This produces a low-germ permeate and a high-germ retentate. The germ concentrate, or retentate, can be concentrated and after a high-temperature heat treatment can be recirculated to the permeate.
ESL Deep-Bed Filtration:
In this method, filter candles made of polypropylene are used. The pore size of the prefilter is 0.3 μm and that of the main filter 0.2 μm. The filtration proceeds at separation temperature and the germs are separated in the depth of the filter without forming retentate. The method sequence of the heating system corresponds to that of the microfiltration.
The product of the method presented is organoleptically comparable with conventionally pasteurized milk. The removal of germs from milk by microfiltration for the purpose of extending shelf life has proved, in principle, to be particularly suitable.
DE 100 36 085 C1 discloses a method for removing germs from milk, in particular in the production of milk for cheese making. For removing germs from milk, the milk is separated into skimmed milk and cream in a separator. Then germs are removed from the skimmed milk by microfiltration or a separator.
U.S. Pat. No. 3,525,629 A discloses a method for sterilizing milk for cheese making. In this method, a bacteria-containing milk slurry is separated off from the milk in a two-step centrifugal method, sterilized, and recirculated to the milk circuit. Such a milk, however, cannot be termed fresh milk.
A two-step centrifugal germ removal is also disclosed in the article “Neuer Stern in der Milchstrasse”, translated as “New star in the milky way”, by Iloi Wasen, Deutsche Molkerei Zeitung, 2003, pp. 40/41. However, specific method sequences are not disclosed in the article.
The document “Separatoren fur Milch-Reinigung and Milch-Entkeimung”, translated as “Separators for milk purification and removal of germs from milk”, by Hanno R. Lehmann and Ernst Dolle as scientific document No. 12 Westfalia Separator AG, Oelde, 1st edition, 1986. FIG. 20 and chapter 3.1.2 disclose two-step removal of germs from skimmed milk. This has the disadvantage that the cream fraction either has a high fraction of spores or, on account of heating, only has a low fraction of β-lactoglobulin.
The present disclosure relates to proceeding from the previous prior art and providing a method for producing fresh milk having a longer shelf life. The embodiments, according to the present disclosure, provide for a method in which no high-temperature heat treatment of the milk or of milk components is necessary.
The present disclosure thus relates to a method for producing fresh milk having a longer shelf life. The method steps include: providing raw milk; and performing an at least two-step centrifugal germ removal process of the raw milk before a standardization process of the raw milk is carried out. The present disclosure also relates to a method for producing fresh milk having a longer shelf life, the method steps including: providing raw milk; performing a first step of a two-step centrifugal germ removal process before a skimming process separating skimmed milk is carried out, and performing a second step of the two-step centrifugal germ removal process during the carrying out of the skimming process separating skimmed milk. The present disclosure also relates to a method of a method for producing fresh milk having a longer shelf life, the method steps comprising: providing whole milk; performing an at least two-step centrifugal germ removal process after a standardization process of the whole milk is carried out.
Thus, in the embodiments of the present disclosure, advantageously, germs are also removed from the cream contained in the fresh milk once, or, also advantageously, twice.
Embodiments of the method of the present disclosure are further discussed and disclosed herein and in the accompanying drawings and claims.
By using an at least two-step centrifugal removal of germs, it is possible to dispense with not only a filtration but also a heating to temperatures of about 125° C. of the raw milk before separation or of the drinking milk after standardization.
The at least two-step centrifugal removal of germs effects a high germ reduction of spoilage-relevant spore formers. For instance, in one liter of milk after the two-step centrifugal germ reduction, at most 1 Bacillus cereus spore per 10 ml of liquid from which germs have been removed, or fewer of these spores, is detectable. Precisely this aerobic spore former increases a hundred fold in a period of 6 days and impairs to a great extent the shelf life of the milk owing to sweet curdling. In this manner, a milk having a longer shelf life is provided which has a shelf life at a storage temperature T≤8° C. in any case up to 21 days and in which it is no longer necessary to add high-temperature heat-treated material in the production. Although an extreme shelf life of 40 days or more is not necessarily achieved, compared with conventional fresh milk, the markedly increased shelf life period of a minimum of 20 days or more, in accordance with the present disclosure, provides a milk having extended shelf life which is not subject to any flavor impairments owing to high-temperature heat treatment. Even the cream does not need to be high-temperature heat treated, but can be if desired.
The lactulose content achieved in the fresh milk having an extended shelf life produced according to the present disclosure, and the content of β-lactoglobulin are comparable with the corresponding contents in fresh milk.
The minimization of germ-rich concentrate, which is removed via the discontinuous emptyings of the separator drum, may, according to the present disclosure, be achieved by using a PRO+ system. That is to say, a system of the type of EP1786565 having fin bodies which are arranged radially outside a disk package of a separator. Thus, it is possible to discharge very small amounts of concentrate arising in a very large emptying interval.
The at least two-stage centrifugal germ removal, in accordance with the present disclosure, can, in addition to the step of skimming, be integrated at various sites into a method for preserving fresh milk. The germ removal steps need not follow one another.
By an additional separation of solids off from the milk during the skimming, likewise a certain discharge of germs from the milk can be effected already. The skimming step, however, is, in this context, only to be considered as a type of preliminary germ removal, but not as a complete germ removal step.
Germ removal, in this context, of the present disclosure, means the targeted treatment of milk or skimmed milk for clarifying from solids, such as germs, spores, bacteria and the like, which includes using a separator, for example, a disk separator.
In this germ removal the liquid phase, or the influent milk, is clarified from solids centrifugally. It is within the scope of the present disclosure to recirculate a substream of the liquid that is clarified in this manner to the feed of the germ removal separator, in order, for example, to further optimize the germ removal effect.
By integrating an at least two-step centrifugal germ removal into the abovementioned production method, an advantageous extension of the shelf life of the milk to a minimum of 20 days can be achieved in accordance with the present disclosure.
It is advantageous when the at least two germ removal steps are already carried out successively before the skimming, that the number of the aerobic germ formers in question has already been drastically lowered, before the various heating processes of, for example, the process steps described herein, to a value below the limit of detection.
In a further embodiment according to the present disclosure, at least one germ removal step can proceed already before the skimming, whereas a second germ removal step is integrated into the method during processing of the skimmed milk.
In a further embodiment according to the present disclosure, germs can be removed from the whole milk in two successive centrifugal steps after standardization. That is to say, after feeding an amount of cream to the skimmed milk.
Whereas the first centrifugal germ removal lowers the number of the corresponding aerobic spore formers by up to 90%, in the later course a separate germ removal from the skimmed milk can proceed in a further centrifugal germ removal step.
To ensure freedom from germs, in this embodiment, it is advantageous if, after the separation step of skimming, the cream is briefly heated to a temperature, for example, of between 100 and 140° C. This is not only to ensure freedom of the cream from germs, but also of the skimmed milk after remixing.
Since freedom of the cream from germs is advantageous in the storage of excess cream, the cream can be heated briefly immediately after the skimming and before the quantitative division, such that germs are also removed from the excess cream.
To ensure freedom from germs during storage of the fresh milk having a longer shelf life, an aseptic packaging, that is known, is advantageous.
Embodiments and working examples, according to the present disclosure, are further discussed herein.
Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings.